Excitatory synaptic boutons in cell culture of mouse spinal cord contain spherical vesicles, while most inhibitory boutons (probably glycinergic in nature) have slightly (but significantly) more ellipsoidal vesicles. A population of boutons with more pleomorphic vesicles also exists in spinal cord cultures. Cerebellar Purkinje cells in culture (probably GABAergic have markedly pleomorphic vesicles in their synaptic terminals. An opiate agonist have been shown to decrease quantal output from dorsal root ganglion cells without affecting post-synaptic responsiveness of spinal cord cells. Chronic blockage of action potentials in developing cell cultures produces a marked deficit in survival, growth and maturation of spinal cord cells. Dorsal root ganglion cells are not affected.